cpu: Define ArchCPU

For all targets, do this just before including exec/cpu-all.h.

Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Acked-by: Alistair Francis <alistair.francis@wdc.com>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

target/s390x/cpu.h

@@ -795,6 +795,7 @@ void s390_init_sigp(void);
 S390CPU *s390_cpu_addr2state(uint16_t cpu_addr);
 
 typedef CPUS390XState CPUArchState;
+typedef S390CPU ArchCPU;
 
 #include "exec/cpu-all.h"